Silicene Nanoribbons Research Articles

Modeling and computation of thermal and optical properties in silicene supported honeycomb bilayer and heterobilayer nanostructures

The compatibility of silicene with the semiconductor technology and its promise in thermoelectric and in optoelectronic devices demands modulation and optimization of its thermal and optical properties using structural modifications. Here we investigate the thermal and optical properties of silicene supported group IV honeycomb bilayer and heterobilayer nanoribbon structures (silicene/germanene and silicene/graphene) using molecular dynamics simulation and first principle calculations. Our modeled silicene/germanene nanoribbons show ~43% lower room temperature average thermal conductivity (2.94 W/m/K) compared to that of similar sized silicene nanoribbons (5.1 W/m/K). Similarly, in silicene/graphene nanoribbons, heterostructuring results in a ~25× reduction of the in-plane thermal conductivity compared to that of a graphene nanoribbon, which is attributed to the phonon confinement in the low frequency region and large mismatch in the phonon frequencies between the monolayers of these heterostructures (~50 THz for the graphene layer and ~11 THz for the silicene layer in the silicene/graphene nanoribbons). We also characterize the temperature and the size dependent thermal conductivity of the modeled structures. The realized low thermal conductivity in these heterostructures could lead to the design of optimized thermoelectrics. Furthermore, we compute the frequency dependent dielectric function and show that the absorption coefficients of our modeled nanostructures are 1.5× to 2× large compared to those of silicene monolayer in the ultraviolet (UV) region, which could be useful in optoelectronic devices such as UV photodetectors. Thus, heterostructuring could be an encouraging route to tune the thermal and optical properties of silicene nanostructures for next generation nano-electronic and optoelectronic devices.

Design of a Low-Power Short-Channel Electrostatically Doped Silicene Nanoribbon FET

In this article, the transfer and output characteristics of an electrostatically doped (ED) 4-armchair silicene nanoribbon (4-ASiNR) field-effect transistor (FET) with three gates are investigated. The numerical simulations are carried out based on the self-consistent solution of the Poisson and Schrodinger equations within the nonequilibrium Green’s function (NEGF) formalism, implemented in the NanoTCAD ViDES simulator. Results show that ED SiNR-FET has better characteristics than chemically doped (CD) SiNR-FET. Additionally, ED-device is inherently free of negative impacts of impurities on the transistor’s performance. The ED SiNR-FET functionality is analyzed using different channel lengths, introducing the extended channel ED-device (ECED) with an improved ${I}_{ \mathrm{\scriptscriptstyle ON}} / {I}_{ \mathrm{\scriptscriptstyle OFF}}$ ratio of $3.8\times 10^{5}$ and a significant ${I}_{ \mathrm{\scriptscriptstyle ON}}$ of 4.6 mA/ $\boldsymbol \mu \text{m}$ . A 15 nm ECED SiNR-FET with an 8 nm channel is studied under different temperatures and supply voltages. Based on the results, low-power (LP) and high-performance (HP) applications are suggested for the ECED-device, with the minimum subthreshold swing of 64 mV / dec and the maximum transconductance of $63~\boldsymbol \mu \text{S}$ , respectively.

Tuning the electronic and magnetic properties of hydrogen saturated zigzag silicene nanoribbon doped with B atoms chain

We performed the first-principles calculations about the electronic and magnetic properties of hydrogen saturated zigzag silicene nanoribbon (HZSiNR) doped with a B atoms chain. The calculated results of formation energies indicate that the doped configurations possess thermodynamic stability. For HZSiNR doped with B atoms chain, a significant transition from semiconducting character to metallic character can occur, which is strongly originated from contributions of B impurities and its connected Si atoms. Moreover, the magnetic state can change from antiferromagnetic state to ferromagnetic state. Meanwhile, the local magnetic moments of Si atoms connected with B atoms are tremendously induced.

Silicene Nanoribbons on an Insulating Thin Film

AbstractSilicene, a new 2D material has attracted intense research because of the ubiquitous use of silicon in modern technology. However, producing free‐standing silicene has proved to be a huge challenge. Until now, silicene could be synthesized only on metal surfaces where it naturally forms strong interactions with the metal substrate that modify its electronic properties. Here, the authors report the first experimental evidence of silicene nanoribbons on an insulating NaCl thin film. This work represents a major breakthrough, for the study of the intrinsic properties of silicene, and by extension to other 2D materials that have so far only been grown on metal surfaces.

Even–odd chain effect and quantum pumping effect induced spatial spin filter on a Y-shaped zigzag silicene nanoribbon junction

We propose a possible spatial spin filter on a Y-shaped zigzag silicene nanoribbon (ZSNR) junction with different even(odd)-chain electrodes by applying three pumping electric fields. By means of the tight-binding model and Keldysh Green’s function method, we calculate the spin-dependent tunneling currents on the middle–left (M–L) and middle–right (M–R) terminals of Y-shaped ZSNR junction, and find that this spin pump not only can generate a pure spin current and a 100% polarized spin current at a zero bias, but also can spatially separate spin up and spin down currents on its even(odd)-chain M–L(R) terminals. The spatial spin filtering phenomena might come from the combination of the even–odd chain effect and single photon-assisted pumping process. The pumped spin up(down) current and its ON(OFF) transport states on M–L(R) terminal of the Y-shaped ZSNR junction can be modulated by almost all the device’s parameters such as the Fermi level, pumping frequency, spin–orbit coupling, staggered lattice potential and magnetization distribution. We also explore the possible way to close the spatial spin filtering behaviors in the device. Our findings might be useful for producing and separating 100% polarized spin up and down currents on multi-terminal silicene nanodevices.

Electronic and thermal properties of silicene nanoribbons: Third nearest neighbor tight binding approximation

In this paper, using DFT calculation and the third nearest neighbor tight-binding model, the electronic properties of the buckled (N,0) armchair silicene nanoribbons (N-ASiNRs) with β-type [N = 9,12,15,…] and γ-types [N = 10,13,16,…] investigated. Also, using the Green’s function method, the nanoribbon width and temperature dependence of the heat capacity [Cv(T)], electrical conductivity [σ(T)], electronic thermal conductivity, and Lorenz factor have been calculated for ASiNRs with β- and γ-types. The required tight binding parameters are obtained based on DFT calculations. Both β- and γ-ASiNRs are direct gap semiconductors and their band gap decreases with increasing the nanoribbon width. Our tight binding calculations show that the band gap of the β type is smaller than that of the γ type, which is in agreement with the DFT results. For both selected nanoribbon types, the thermal properties increases with temperature due to the band gap modifications and getting the thermal energy by charge carriers. We found that the thermal properties of β configuration are larger than that γ configuration and their differences increases with increasing the temperature.

Enhanced negative differential resistance in silicene double-barrier resonant tunneling diodes

We investigate the transport properties of double-barrier resonant tunneling diodes based on silicene nanoribbons by means of transfer matrix method under the external electric field. It is found that the transmission shows resonance suppression (enhancement) under the positive (negative) bias. The spin-dependent and valley-dependent negative differential resistance (NDR) characteristics are found both in the symmetric and asymmetric structures. The influence of various factors on the I-V characteristics is analyzed, it is found that the NDR characteristics can be greatly enhanced by the structural parameters, Fermi energy, and band gap. What should be laid stress on is that the maximum peak-to-valley ratio (PVR) can reach up to 13 by regulating the band gap. Proposed structure here could be the base of other high-frequency electronics devices.

Performance analysis of functionalized silicene nanoribbon‐based photodetector

AbstractIn this work, performance analysis of functionalized silicene nanoribbons‐ (SiNRs) based photodetector is evaluated using Atomistix Tool kit software. The functionalized SiNRs were obtained by co‐decorating them with lithium atoms on one side and chlorine atoms on the other side. The performance of photodetector is analyzed in terms of spectral response, responsivity and detectivity, which are found to be <450 nm, 8.33 × 103 AW−1, and 4.94 × 1012 Jones, respectively. In addition, the calculated results were compared with modern photodetectors based on other materials. The comparative study reveals that the proposed device offers better performance than these photodetectors. Therefore, the modeled device will find a number of potential applications in optoelectronics.

Band bending and zero-conductance resonances controlled by edge electric fields in zigzag silicene nanoribbons

We study the band structure and transport property of a zigzag silicene nanoribbon when electric fields are applied to the edges. It is found that band bending could be induced and controlled by the antisymmetric edge fields, which can be understood based on the wave functions of the edge states. The highest valence band and the lowest conduction band coexist in the band-bending region. With the narrowing of edge potentials, the bending increases gradually. When the edge fields become symmetric, an asymmetric band gap at the Dirac points can be obtained due to the intrinsic spin-orbit interaction, suggesting a valley-polarized quantum spin Hall state. The gap could reach a maximum value rapidly and then decrease slowly as the electric fields increase. Due to the combining effect of the band bending, band-selective rule, and resonant states, many zero-conductance resonances and resonance peaks appear in different regions, which could be described by the Fano resonance effect. Furthermore, the band bending and zero-conductance resonances are robust against the Hubbard interaction. The Hubbard interaction could work as a spin-dependent edge field, together with the edge electric fields, leading to a spin-dependent band gap and various quantum phases such as metal and half-metal.

Impact of Width Scaling and Parasitic Series Resistance on the Performance of Silicene Nanoribbon MOSFETs

The performance of 15-nm-gate-length MOSFETs based on silicene nanoribbons (SiNRs) is analyzed with respect to width scaling, series resistance, and ballisticity of electron transport. Numerical simulations were based on quantum transport with atomic resolution of nanoribbon Hamiltonians and their bandstructure. Assuming negligible tunneling, we found that SiNR MOSFETs in which the nanoribbons are wider than 2.8 nm can fulfill the requirements set by the International Roadmap for Devices and Systems (IRDS) for the “3-nm” logic node even with 50% ballisticity and parasitic series resistance of $270~\Omega \mu \text{m}$ .

2D Honeycomb Silicon: A Review on Theoretical Advances for Silicene Field-Effect Transistors

Catalysed by the success of mechanical exfoliated free-standing graphene, two dimensional (2D) semiconductor materials are successively an active area of research. Silicene is a monolayer of silicon (Si) atoms with a low-buckled honeycomb lattice possessing a Dirac cone and massless fermions in the band structure. Another advantage of silicene is its compatibility with the Silicon wafer fabrication technology. To effectively apply this 2D material in the semiconductor industry, it is important to carry out theoretical studies before proceeding to the next step. In this paper, an overview of silicene and silicene nanoribbons (SiNRs) is described. After that, the theoretical studies to engineer the bandgap of silicene are reviewed. Recent theoretical advancement on the applications of silicene for various field-effect transistor (FET) structures is also discussed. Theoretical studies of silicene have shown promising results for their application as FETs and the efforts to study the performance of bandgap-engineered silicene FET should continue to improve the device performance.

Band gap determination of graphene, h-boron nitride, phosphorene, silicene, stanene, and germanene nanoribbons

The energy band gap of graphene, h-boron nitride, stanene, silicene, germanene, and phosphorene nanoribbons is investigated theoretically with two approaches. In the first approach, a set of equations to calculate the energy band gap of nanoribbons is deduced using the expression of Fermi velocity. The size dependency of the energy band gap so obtained confirms previous expressions. The second approach, however, determines resistivity by directly connecting quantity to the energy band gap using an electron–acoustical phonon scattering mechanism. For the calculation of the energy band gap and resistivity, the armchair configuration of nanoribbons is considered. It is observed that the transverse magnetic field influences the energy band gap and resistivity. The magnitude of the band gap is negative up to a certain value of the field and turns positive at a sufficiently higher field. The negative band gap can be interpreted as metallic behavior of the materials. The results of the work are useful in the determination of the energy band gap of nanoribbons for their nanoelectronic and optoelectronic applications as well as tuning the band gap using the applied magnetic field.

Investigation on the Effect of Gate Dielectric and Other Device Parameters on Digital Performance of Silicene Nanoribbon Tunnel FET

In this article, silicene nanoribbon (SiNR)based tunneling field effect transistor (TFET) is investigated for low power digital applications. A comprehensive study on the role of gate dielectric and device parameters, such as drain doping, channel length of SiNR TFETs, are carried out to see the performance of digital applications. To achieve higher ION/IOFF ratio and lower subthreshold swing (SS), a detailed investigation is carried out on the equivalent oxide thickness (EOT), channel length, and doping of drain. A digital performance metric comparison of SiNR TFETs with germanium-silicon (Ge-Si), monolayer graphene nanoribbon (MLGNR), and bilayer graphene nanoribbon (BLGNR) TFETs has been performed. It is concluded that SiNR TFETs made of Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> gate dielectric with 0.86 nm effective oxide thickness, 0.5 mM (8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ) drain doping concentration, and 5 mM (8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ) source doping concentration exhibits lower intrinsic delay, higher ION, higher ION/IOFF ratio, and lower SS at 25 nm channel length.

Electronic properties of zigzag silicene nanoribbons with single vacancy defect

&lt;p&gt;Silicene is envisaged as one of the two-dimensional (2D) materials for future nanoelectronic applications. In addition to its extraordinary electronic properties, it is predicted to be compatible with the silicon (Si) fabrication technology. By using nearest neighbour tight-binding (NNTB) approach, the electronic properties of zigzag silicene nanoribbons (ZSiNRs) with single vacancy (SV) defects are modelled and simulated. For 4-ZSiNR with L=2, the band structures and density of states (DOS) are computed based on SV incorporated ZSiNRs at varying defect locations. The results show that the SV defect will shift the band structure and increase the peak of DOS while the bandgap remain zero. This work provides a theoretical framework to understand the impact of SV defect which is an inevitable non-ideal effect during the fabrication of silicene nanoribbons (SiNRs).&lt;/p&gt;

Electronic properties of zigzag silicene nanoribbons with single vacancy defect

Electronic properties of zigzag silicene nanoribbons with single vacancy defect

First-principle study on the quantum transport in an armchair silicene nanoribbon-based [formula omitted] diode

Using the first-principle calculations, we study the electronic band structure, density of state (DOS), effective mass, quantum capacitance, transmission spectrum, and current–voltage characteristic of armchair silicene nanoribbons (ASiNRs) doped with aluminum (Al) and phosphorus (P) atoms. ASiNR is an intrinsic semiconductor, and depending on the type of impurity atoms applied, it becomes an n-type and p-type semiconductor. Our numerical results show several open energy windows and different peaks in the transmission spectra under various applied bias. These effects cause nonlinear behavior in the current–voltage curves. Also, the value of current density for four samples is obtained as Jpure>JAl>JP>JAl&P at a fixed voltage. The threshold voltage for these samples are given as Vpureth>VAlth>VPth>VAl&Pth. The effective masses of carriers increase in the pure and doped ASiNR systems are calculated from the band structures spectra. Moreover, the quantum capacitance of the pure and doped ASiNR is investigated for direct and reverse biases. The results of this work may be useful in novel phenomena such as nanoelectronics applications and near-infrared photodetectors.

Methylation Detection and DNA Sequencing Based on Adsorption of Nucleobases on Silicene Nanoribbon

Nanodevices based on two-dimensional materials hold great promise for DNA sequencing. Owing to some unique properties, silicene has become a potential alternative to the well-known graphene as a se...

Tuning the thermoelectric response of silicene nanoribbons with vacancies

In this work, we present a thorough study of the thermoelectric properties of silicene nanoribbons in the presence of a random distribution of atomic vacancies. By using a linear approach within the Landauer formalism, we calculate phonon and electron thermal conductances, the electric conductance, the Seebeck coefficient and the figure of merit of the nanoribbons. We found a sizable reduction of the phonon thermal conductance as a function of the vacancy concentration over a wide range of temperature. At the same time, the electric properties are not severely deteriorated, leading to an overall remarkable thermoelectric efficiency. We conclude that the incorporation of vacancies paves the way for designing better and more efficient nanoscale thermoelectric devices.

Even-odd chain effect and perpendicular electric field induced spin valve in a zigzag silicene ferromagnetic junction

We study the spin transport in a zigzag silicene nanoribbon (ZSNR) ferromagnetic junction with different even(odd)-chain widths and a perpendicular electric field on its drain electrode. By using the tight-binding lattice model and Keldysh Green’s function method, we calculate the spin-dependent transverse conductance and find that the spin switching effect always exists in the system regardless of the zigzag chain number is an even or an odd. The spin valve phenomena come from the combination of the even-odd chain effect and the perpendicular electric field induced energy gap. When a transmission electron flows from the left lead to the middle scattering region, the transport exhibits a peculiar even-odd chain effect, and then the electron may be prohibited to pass through the middle-right tunneling junction when a perpendicular electron field is applied on the right terminal. The spin transport in the proposed device can be controlled by almost all the system parameters such as Fermi energy, electric field, spin orbit coupling, ferromagnetic magnetization and width of the ZSNR. Furthermore, the proposed device might act as an electrical tunable spin valve to produce and detect a 100% polarized spin current.

Photoinduced anisotropic edge states and signatures of nonequilibrium spin polarization in silicene nanoribbons

Most topological phase transitions are accompanied by the emergence of surface/edge states with spin dependence. Usually, the quantized Hall conductivity cannot characterize the anisotropic transports and spin dependence of topological states. Here, we study the intricate topological phase transition and the anisotropic behavior of edge states in silicene nanoribbon submitted to an electric field or/and a light irradiation. It is interesting to find that a circularly polarized light can induce a type-II quantum anomaly Hall phase, which is manifested as the high Chern number and the strong anisotropic edge states. Besides the measurement of the quantized Hall conductivity, we further propose to probe these topological phase transitions and the anisotropy of edge states by measuring the current-induced nonequilibrium spin polarization. It is found that the spin polarization exhibits more signatures about the behavior of surface/edge states, beyond the quantized Hall conductivity, especially for spin-dependent transports with different velocities.